Write a java program that compiles under the command line that reads from standard input an operation in NPN.

You can assume there is a space between every operator and number. Your program should be able to correctly handle the operators +,-,*,/.

Every number will be a 32 bit non-negative integer.

Be careful that your program recognises precisely the three characters above (plus sign, minus sign, and the lowercase letter x, respectively).

You may NOT use any Java standard library class or method other than for input/output.

Other examples of NPN formulas are:

3 ( result is 3)

x 2 0 (result is 0)

x + 2 3 + 2 2 (result is 20)

+ x 2 3 4 (result is 10)